Three liquids of densities \[d,\,2d\] and \[3d\] are mixed in equal proportions of weights. The relative density of the mixture is

• A.            \[\frac{11d}{7}\]                 
• B.            \[\frac{18d}{11}\]
• C.            \[\frac{13d}{9}\]                 
• D.            \[\frac{23d}{18}\]